Ms. Deshields took the baby from the man at his home on the 2400 block of Wylie Avenue in the Hill District at about 6:10 p.m., the commander said. The relationship between the man and woman, and man and infant, was not immediately known.

The woman, who is black, stands 5-foot-6 and weighs about 140 pounds. She has brown hair, possibly in a ponytail, and is wearing pink pants. Cmdr. Stangrecki said she may be in a gold car or van.

Police ask those with information on Ms. Deshields' location to call 911.